On Wed, Jun 29, 2011 at 11:20 AM, Muli Ben-Yehuda <[email protected]> wrote: > Is it feasible to build a contemporary Linux system with around 1 > million distinct user UIDs? Anyone tried it? We can assume only a > relatively small subset of users will actually be logged in at once.
Formally, the kernel supports 2^32 users (since 2.6 - widening the uid type to 32-bit was one of the changes from 2.4, but I assume you know that better than I do :). I assume you are more interested in the practical aspects. All the comments regarding a DB behind authentication are very valid. Besides that, I would expect that the real limitation will be your definition of "a relatively small subset" of simultaneous logins. Say you have 1M users. Do you expect a hundred being logged in at the same time? A thousand? 10K? What will their workload be? For each login resources are allocated. Each user will consume threads, file descriptors, network ports, you name it. I expect you'll hit some limits for a relatively small number of users. Especially if you let users start multiple shell sessions that may be counted as separate "logins". If you decide to try an experiment you will probably need to look at both system defaults and the default PAM configuration (the latter may have relevant limits configured, and you may want to change them). I would expect a beefy system with 1M distinct IDs (in a DB, etc.) and <100 (to feel safe) concurrent users to be feasible. An interesting variant may be a big farm of Linux machines with 1M distinct users in a central DB and a scheme where a login process will include an allocation of a machine and mounting the user-specific data volumes (/home) on that machine, "on demand" (khmm... you know what I mean). -- Oleg Goldshmidt | [email protected] _______________________________________________ Linux-il mailing list [email protected] http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
